The Effect of Different Planetary Boundary Layer Schemes on the Simulation of Near Surface O₃ Vertical Distribution

Located at the base of the troposphere and affected strongly by ground surface, the planetary boundary layer (PBL) is the main passage of air-land interaction and air pollution. The PBL affects the momentum and heat exchange between the ground and atmosphere through the surface force and turbulence transport. The concentration of pollutants on the ground depends on the vertical mixing state of the atmosphere. Thus, the boundary layer parameterization scheme is not only the important part of numerical model for weather forecast, but also the important foundation of air pollution numerical model. A variety of boundary layer parameterization schemes of physical process are developed, which have different effects on the ground meteorological field and pollutant diffusion. To further understand how the boundary layer processes affect the mixing and transport of air pollutants, a sensitivity experiment is designed and the WRF-Chem model with different PBL schemes (MYJ, YSU and ACM2) is utilized to simulate the PBL structures and O₃ vertical distributions on a cloudless and steady day (26-27 Aug 2013). Simulations of temperature field and wind speed field using different PBL schemes are compared to observations. The analysis focuses on the difference of simulations of residual layer formation at night and O₃ vertical distribution after sunrise using different PBL schemes. Simulations are compared with the radiosonde data of ozone at Gucheng Station. Results show that the regional distribution characteristics and vertical structures of the temperature and wind speed can be well simulated by all these three PBL parameterization schemes, but the simulation of the ground temperature and wind speed are generally on the high side. The nighttime boundary layer height simulated by MYJ scheme is much higher than those simulated by YSU and ACM2 schemes, leading to the difference in near surface pollutants concentration. In the evolution process of the boundary layer structure from stable state in nighttime to slightly disturbance state after sunrise, the vertical temperature and wind structures simulated by YSU and ACM2 schemes are more consistent with observations. Simulations on effects of boundary layer process upon O₃ vertical distribution using YSU and ACM2 schemes also have obvious advantages over MYJ scheme. It should be noted that the simulation is only on a clear and steady weather case, and for complex weather conditions, effects of boundary layer schemes need further verification.